Location and General Description

The Sunda Shelf mangroves are found on the island of Borneo, fringe of the Riau Archipelago and the east coast of Sumatra. This mangrove ecoregion occurs on portions of the coastline of Malaysia, Brunei and Indonresia.The climate and physical conditions vary widely in this region, giving rise to a high diversity of plant and animal species found in these forests. However, the region generally has high humidity, seasonal wind and precipitation, high temperatures, and high annual rainfall. Tidal fluctuations have large variations over short distances.

Source: WWF

There are five major mangrove types, or consociations, recognized in this region, based on the dominant species within the genera of Avicennia, Rhizophora, Sonneratia, Bruguiera, and Nypa. The relative occurrence of each type is based on fluctuations in soils, salinity, and the tidal regime. Typically mangroves display a zonation or succession of forests, with each zone being dominated by one of the consociations. On the seaward sediments, Avicennia-Sonneratia forest dominates. Moving inland, there is softer and deeper mud sediment dominated by Rhizophora-Bruguiera forests. Further inland, the soils become firmer and the forests display a greater species diversity. In areas with a substantial freshwater influence, Nypa palms dominate. Mangrove forests reach 50 metres (m) in height in many areas.

Biodiversity Features

Mangrove diversity in terms of endemics or richness is not great. More than 250 birds are listed for this ecoregion, but many of them are transitory, some migrants, and some year-round inhabitants. Determining an exact count for this diverse ecoregion is difficult because of the transitional nature of the habitat.

The mangroves of Borneo are home to the Proboscis monkey (Nasalis larvatus), which is one of the few large mammals limited to mangrove and peatswamp forest habitats. Proboscis monkeys eat primarily young leaves and the seeds of unripe fruit. To digest this diet, they have developed highly complex sacculated stomachs with specialized bacteria.

Although mangroves lack outstanding species diversity, they provide vital ecological functions by being at the interface between the terrestrial and marine realms. Mangroves stabilize coastlines from erosion, accumulate sediment, and provide a nursery for numerous coastalfishes.

Last Glacial to Holocene Perspective

Pollen core research yields important information on the ecological change to the Sunda Shelf region over the last 25,000 years. During the Last Glacial Maximum sea levels were approximately 120 metres lower along the Sunda Shelf, leaving much of the present seabed to serve as a landbridge to near-shore islands.
Aerial prop roots for mangroves on the foreshore,Bako NP. @ C.Michael Hogan

The Holocene itself can be viewed to have an early segment (9900 to 5200 years before present; a middle segment (5200 to 2300 years before present); and a recent segment (2300 years before present to current time). The early Holocene segment witnessed sharp increases in mangrove species, especially for the Sonneratia and Rhizorora genera; at this same time montane rainforests almost disappeared from the region. The combination of these trends indicate that there was a pronounced warming that apparently endured through the mid-Holocene.

During the recent Holocene mangrove swamps and lowland rainforests declined on the Sunda Shelf, based upon pollen core records. During this recent epoch montane rainforests flourished along with ferns (especially Dicranopteris and Acrostichum genera). Pinxian Wang interprets the latter occurrences as due to a cooling climate and to human deforestation, pursuant to analysis by Li and Sun.

Current Status

Traditionally, mangroves have been harvested for fuelwood, charcoal, and timber, and, in some instances, these practises have been done sustainably. However, in recent decades mangroves have been severely degraded by deforestation, agriculture, urban development, fishing, and shrimp farming despite the many protected areas that include mangrove forests (table 1).

Table 1. Protected Areas That Overlap with the Ecoregion.

Protected Area

Area (km2)

IUCN Category

Kuala Jambu Aye/Air

140

PRO

Kuala Langsa

140

PRO

Bakau Selat Dumai

190

PRO

Pulau Burung

190

I

Berbak

200

II

Bakau Muara Kampar

350

PRO

Tanjung Datuk

130

PRO

Kelompok Hutan Bakau Pantai Timur

90

I

Kulamba

230

VI

Muara Kayan

320

PRO

SAR (Sanctuary Reserve)

50

II

SAR (Sanctuary Reserve)

340

UA

SAR (Sanctuary Reserve)

30

PRO

SAR (Sanctuary Reserve)

40

II

Hutan Sambas

20

PRO

SAR (Sanctuary Reserve)

50

IV

Muara Kendawangan

290

PRO

Unnamed

60

?

Tanjung Penghujan NR

170

PRO

Tanjung Puting

190

II

Kelompok Hutan Kahayan

560

PRO

Pamukan

320

PRO

Teluk Kelumpang Selat Laut/Sebuku

880

I

Pleihari Tanah Laut

410

IV

Apar Besar

1,000

PRO

Pantai Samarinda

140

PRO

Total

6,530

Protected areas have not addressed many of the conversion threats facing mangrove systems. Many protected areas have been encroached upon for consumptive uses and have not afforded real protection in recent decades.

Types and Severity of Threats

Bako National Park, Malaysia. Source: WWF and Canon
The threats to the habitat remain the same as those that already have claimed vast areas of land: deforestation, aquaculture, agriculture conversion and urbanization.

Many mangroves reside in logging concessions or are being cut down for commercial charcoal production. Production of woodchips and pulp is increasing, and more chip mills are being built. Shrimp farming continues to threaten vast mangrove forests. Other aquaculture practices include cockle culture and exploitation of the finfish, bivalve and crab fisheries. Water pollution, agriculture conversion, and oil extraction also threatened mangrove forests.

Additional Information on this Ecoregion

For a terser summary of this entry, see the WWF WildWorld profile of the Sunda Shelf mangroves ecoregion.

See Also

Disclaimer: This article contains certain information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content .